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    <title>Document</title>
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    <script>

        var n = 1 ;
        var m = 1 + 1 ;

        var x = 1 / 0 ;
        console.log(x) ;    // Infinity

        console.log(typeof x) ;  // number

        console.log(Boolean(x)) ;

        var y = 1 / 'a' ;
        console.log(y) ;   // NaN    not a number   非数字的集合
        console.log(typeof y) ;   // number



        // 数字
        //   常规的数字
        //   1 / 0    Infinity  无穷
        //   NaN


    </script>
    
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